In general, a brake system increases a force, which is applied to a brake pedal by a driver, to brake a moving vehicle. Since the brake system simply stops a rotating wheel to prevent the wheel from being rotated, it is difficult to obtain an optimum braking performance corresponding to running conditions of a vehicle and road conditions.
An anti lock brake system, which appropriately adjusts braking pressure applied to the wheel on the basis of a slip rate calculated from wheel speed so as to prevent the wheel from being locked, or a traction control system is used to overcome the limitation of the above-mentioned simple brake system, which makes it possible to improve the stability of a vehicle.
In particular, a TCS system prevents a vehicle from being unexpectedly rotated (for example, on an icy road) while pumping oil from a master cylinder to provide braking pressure to a wheel independent of a brake line that is provided between a master cylinder and a wheel and supplies braking pressure. In this case, a traction control valve (TCV) is used to form oil passages between the master cylinder and a pump and between the master cylinder and a wheel cylinder.
That is, when the TCS (or ESP: Electronic Stability Program) system is operated, the TCV controls the flow of brake oil between the master cylinder and an oil pump, and between the master cylinder and a wheel cylinder provided in a wheel. Accordingly, the TCV controls oversteering or understeering corresponding to friction between a tire and a road surface, and improves the stability and steerability of a vehicle.
Further, the TCV should have a quick pressure rising function during normal braking, a quick pressure releasing function during a brake release, and a pressure maintaining function capable of controlling the wheel cylinder during the operation of the TCS (or ESP) while closing a channel between the master cylinder and the wheel cylinder.
For this reason, a pressure rise channel with a check valve is further formed in the TCV so that braking oil pressure can be quickly increased from the master cylinder to the wheel cylinder. In general, the TCV is operated while pressure of 100 bar or less is generated.
As described above, the TCV should quickly induce oil flow in order to always have excellent responsiveness, and sufficiently maintain high pressure and low pressure. In particular, there is a demand for the following TCV. The TCV maintains required pressure in a valve body and does not decrease responsiveness during a low pressure control where a channel corresponding to the master cylinder is closed and a wheel cylinder is controlled when the brake pedal is not operated and the TCS (ESP) is operated.